1. Field of the Invention
The present invention generally relates to a rotary machine having a stator core with exposed outer circumference, and to a process for manufacturing such a rotating machine.
2. Description of the Prior Art
FIG. 1 is a side view partly in longitudinal section showing a conventional electric motor and FIG. 2 is a front view of a lamination of a laminated stator core employed in the electric motor shown in FIG. 1.
Referring to FIGS. 1 and 2, there are shown a laminated stator core 1 formed by a plurality of stator core laminations having a thickness of about 0.5 mm, a stator coil 2 wound on the stator core 1 and end plates 3 attached respectively to both ends of the stator core 1, brackets 4 formed of a steel plate, fastened to the stator core 1 by through bolts 5 and nuts 6, and holding bearings 7 in their bearing outer ring portions, a shaft 8 supported by the bearings 7, and a rotor core 9 fixedly mounted on the shaft 8.
The stator core 1 and the end plates 3 are welded by tungsten inert gas welding (hereinafter, referred to as "TIG welding") while they are compressed. Then, a stator core 1, i.e., the assembly of the stator core 1 and the end plates 3, is subjected to finish machining (hereinafter, referred to as "sizing") to machine the end plates 3 to a size and shape conforming to those of the corresponding portions of the brackets 4. The bearing portions for holding the bearings 7 and end plate receiving portions of the brackets 4 are also machined. In assembling the electric motor, the stator assembly of the stator core 1, end plates 3 and wound stator coil 2 on the stator core assembly and the brackets 4 are fastened together the brackets 4 by the through-bolts 5 and the nuts 6. The nuts 6 may be substituted by threaded holes formed in one of the brackets 4.
This electric motor is not provided with any housing to cover the stator core 1, and the outer circumference of the stator core is exposed.
Thus, the conventional electric motor is manufactured by individually subjecting the assembly of the stator core 1 and the end plates 3 welded to both ends of the stator core 1, and the brackets 4 to sizing, and fastening the brackets 4 to the stator assembly (stator core 1, end plates 3 and stator coil 2) with the through-bolts 5 and the nuts 6. Accordingly, such a conventional electric motor and the process of manufacturing the same have the following problems.
(1) It is difficult to assemble the stator core 1 and the end plates 3 with the bore of the stator core 1 and the bearing portions of the brackets 4 disposed relative to each other at a high concentricity. The sizing of the end plates 3 with reference to the bore of the stator core 1 and the sizing of the bearing portions of the brackets 4 for holding the bearings 7 are performed separately. Consequently, machining error in the end plates 3 and in the bearing portions of the brackets 4 are accumulated. The accumulated error is greater than the machining error in the bearing portions of the brackets 4 relative to the bore of the stator core 1 when the bearing portions of the brackets 4 are sized directly with reference to the bore of the stator core 1.
(2) The holes in the stator core 1 for receiving the through-bolts 5 require an additional area, which increases the quantity of material for forming the stator core 1 and increases the weight and cost of the electric motor.
(3) In joining together the assembly of the stator 1 with the end plates 3 and the brackets 4, a liquid sealant is applied to the joining surfaces of the end plates 3, and then the brackets 4 are fastened to the assembly of the stator core 1 and the end plates 3. If the liquid sealant is applied irregularly to the joining surfaces of the end plates 3 or if the application of the liquid sealant is forgotten, the insulation of the electric motor is deteriorated by the leakage of external liquids such as a grinding coolant into the electric motor.
(4) When one of the four through-bolts 5 is loose, the mechanical strength of the electric motor to withstand a bending force, such as the tension of a belt acting on the rotor shaft 8, and the rigidity of the motor are reduced, then and the parts of the electric motor thus resonate with external vibrations to generate noise.